erosion analysis of subsea equipment: a case study with high solid loading

1 © 2013 ANSYS, Inc. September 19, 2014 ANSYS Confidential

Erosion Analysis of Subsea Equipment: A Case Study With High Solid Loading

2014 Convergence Conference

Uday Godse, Prospect Flow

energy engineering

Erosion analysis of Subsea equipment

A case study with high solid loading

Presented by: Uday Godse, PhD, P.E

QMF 21 Rev 3

Content

• Prospect introduction

• Fundamentals of erosion analysis

• Erosion models used in CFD

• Low sand loading – Examples

• Moving deforming mesh (MDM) by Ansys-Fluent

• A case study with high solid loading

– Approach

– Results

• Summary

22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 2

QMF 21 Rev 3

Prospect introduction

• Leaders in engineering, design and analysis providing solutions to

the upstream oil and gas industry and wider energy sector since

1999

• Prospect global locations

– Houston

– Aberdeen

– Derby

– Stavanger^

– Dubai^

^ WWC 22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 3

QMF 21 Rev 3

Prospect’s value


EN

GIN

EER

ING

CA

LC

S

DESIG

N C

OD

ES

PH

YSIC

AL T

EST

ING

CO

MPU

TA

TIO

NA

L A

NA

LYSIS

Engin

eerin

g Insigh

t

Experience

QMF 21 Rev 3

ANSYS history & usage

• An ANSYS customer since 1999

• Fluent – Gas Dispersion

– Multi-phase flow

– Thermal analysis

– Erosion prediction

• Mechanical

• Work bench

• AQWA


QMF 21 Rev 3

Flow analysis capabilities


• Prospect routinely analyses thermal behaviour of subsea

components, gas dispersion, multiphase separators, containment

systems used during emergency response

• Prospect has over 10 years experience in predicting flow induced

erosion and has used advanced methods such as computational

fluid dynamics extensively throughout that period

• Prospect has successfully completed over 70 erosion prediction

jobs for a range of clients placing at the forefront of erosion

prediction in the oil and gas industry

Fundamentals of erosion analysis

QMF 21 Rev 3

Background

• Accurate erosion predictions are very critical to risk

management studies

• Erosion of wall material is mainly due to the cutting action or

repeated plastic deformation caused by the particles impacting

the wall

• Erosion damage depends on impact parameters and mechanical

properties of the material

• The impact parameters include impact angle, impact velocity and

size, shape and density of the particles under consideration

• The mechanical properties include density and material hardness

of the material

• Erosion predictions range from simple to very complex


QMF 21 Rev 3

Approaches

• API 14E

• DNV RP O501

or Tulsa E/CRC

• CFD


𝑣𝑒=

𝑐

𝜌𝑚

Incr

eas

ing

com

ple

xity

QMF 21 Rev 3

Erosion models

• Prospect has experience with the primary erosion models used

in the oil and gas industry:

– Tulsa Model

– DNV

– Oka

• All of these models have a similar form


)()( 59.0 fVFBHCe n

psr

n

ref

p

sru

u)(fKe

21 n

ref

p

n

ref

p

refrd

d

u

u)(fee

QMF 21 Rev 3

Erosion vs. Angle of impact

• Most industry accepted models for erosion include an angle

function to reflect the influence of impact angle, f(alpha)

• A typical example is shown

• As can be seen, angle function is very sensitive to the type of

material


0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40 50 60 70 80 90 100

Brittle

Ductile

Angle

QMF 21 Rev 3

Typical erosion problems


• CFD can tackle any flow geometry but is most typically used to

examine the following types of equipment:

– Trees and flow lines

– Chokes

– General pipe networks

• CFD can tackle any flow conditions such as:

– Production flow – light sand loading

– Frac flows & well kills – heavy sand/particle loading

– Blow out conditions – extreme flow conditions

• CFD can address erosion wear and its effect on erosion rate

QMF 21 Rev 3

General flow networks


Normalized

Erosion Rate 1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

CONTOURS OF EROSION RATE

QMF 21 Rev 3

Erosion in Plug tee


2.74 mm/yr

1.71 mm/yr

CONTOURS OF EROSION RATE ON PLUG TEE

FLOW

[mm/yr]

QMF 21 Rev 3

Erosion of pristine geometry


IMAGE SHOWING THE CONTOUR OF EROSION RATE [mm/hr]

PEAK EROSION

RATE 14.43 MM/HR

SECONDARY EROSION

RATE ~ 3.5 MM/HR

QMF 21 Rev 3

Erosion of worn geometry


IMAGE SHOWING THE CONTOUR OF EROSION RATE [mm/hr]

PEAK EROSION

RATE 5.33 MM/HR

SECONDARY EROSION

RATE ~ 2 MM/HR

QMF 21 Rev 3

Pristine vs. Eroded geometry


Initial particle trajectory

Particle trajectory for eroded wall

Low sand loading – Production scenario

QMF 21 Rev 3

Low sand - 5D bend test


0

0.0000005

0.000001

0.0000015

0.000002

0.0000025

0.000003

0.0000035

0 10 20 30 40 50 60 70 80 90

Ero

sio

n R

ate

(m

/kg s

an

d)

Ang le round bend (Degrees)

CFD

DNV Test

Flow conditions:

Inlet mixture velocity: 36.3 m/s

Mixture density: 72.3 kg/m3

Mixture viscosity: 1.8E-5 kg/m-s

Pipe ID: 26.5 mm

Particle size: 250 micron

Sand volume fraction < 1%

Low sand loading – Fracking scenario

QMF 21 Rev 3

Fracking – Inlet manifold


INLET MANIFOLD SHOWING ORIGINAL CAD (LEFT) AND SIMPLIFIED GEOMETRY (RIGHT)

SLURRY INLET

WATER INLET

OUTLET

REGION OF POTENTIAL

EROSION

WATER INLET

WATER INLET

Flow conditions:

Fluid flow rate: 16 m3/min

Fluid density: 1017 kg/m3

Fluid viscosity: 4 cP

Sand rate: 26 kg/s


Sand volume fraction: 4%

QMF 21 Rev 3

Fracking – Steady-state


mm/min

Manifold after 24 days

Maximum eroded depth: 18 mm

CFD predictions

Extrapolated depth: 1140 mm

CFD predictions >> Measurements

IMAGE SHOWING THE CONTOUR OF EROSION RATE [MM/MIN]

QMF 21 Rev 3

Erosion - Moving deforming mesh

• The erosion rates predicted using a steady-state system can be

very conservative and may or may not represent reality

• For more accurate predictions of erosion rate there is a need to

account for the change in wall position

• Erosion-MDM coupling module is available in Ansys-Fluent

• The erosion module dynamically changes the surface wall

position based on the erosion at regular time intervals

• The wall face nodes are moved by a distance based on the

erosion rates

• The erosion study was re-visited using the erosion-MDM module

and the results are presented next


QMF 21 Rev 3

Fracking scenario – Erosion MDM


After 6 hrs

~2 mm

After 12 hrs

~4 mm

After 18 hrs

~5.6 mm

After 24 hrs

~6.8 mm

m

IMAGE SHOWING THE CONTOUR OF CUMULATIVE ERODED WALL DISTANCE [M]

QMF 21 Rev 3

0

2

4

6

8

10

12

14

16

0 4 8 12 16 20 24 28 32 36 40 44

Peak

ero

sion [

mm

]

Frac time [Hrs]

CFD-Steady State CFD-MDM

Fracking scenario – Extrapolated CFD data


CFD (steady state) >> Measurements

CFD (MDM) ~ Measurements

1140 mm vs. 32 mm

Extrapolation

Extrapolation

QMF 21 Rev 3

Fracking scenario – Summary

• Steady-state analysis using linear extrapolation can yield order of

magnitude conservative erosion rates

– 1140 mm vs. 18 mm Measured value

• Erosion-MDM module in Ansys-Fluent is a viable option for

better erosion estimates

– 32 mm vs. 18 mm Measured value


High sand loading – Well kill scenario

QMF 21 Rev 3

Well kill scenario – Simple elbow test

• A case study with high solid loading (~40% solid by volume)

representing a well kill scenario is presented next

• A simple elbow has been considered for this study

• Prospect has been involved in multiple validation studies at the

moment to validate the CFD analysis against the test data with

high solid loading

• The modeling approach is presented next

• The approach is followed by some normalized results after few

hours of operation


QMF 21 Rev 3

Approach

• Eulerian granular multiphase model was utilized to account for

the particle-particle and the particle-fluid phase interactions

• Moving deforming mesh module was utilized

• Due to high solid loading the particles travel nearly parallel to the

wall surface and hence erosion due wall shear stress is more

dominant than erosion due to particle impact

er_shear = A (Vp)n SS


• In order to account for both erosion mechanisms (wall shear and

impact based erosion), the combined effects of both the models

were considered:

er_total = er_impact + er_shear

QMF 21 Rev 3

Well kill scenario – Eroded distance


ORIGINAL GEOMETRY

Normalized

Eroded distance

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

DEFORMED GEOMETRY

Flow conditions:

Inlet velocity: 25 m/s

Fluid density: 1800 kg/m3

Fluid viscosity: 50 cP


Solid volume fraction: 40%

QMF 21 Rev 3

Well kill scenario – Erosion rates


IMPACT BASED RATES

Normalized

Erosion rates

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

SHEAR BASED RATES

Hot spot on turn will

reduce as flow continues

to erode the turning edge

Shear will continue

contributing and will become

the primary erosion

mechanism as flow continues

QMF 21 Rev 3

Well kill scenario – Summary

• Well kill scenario is a work in progress

• High-solid loading needs special treatment on account of the

erosion induced due wall shear stress

• Abrasive (shear stress) erosion model in Ansys-Fluent can

account for the wall shear stress induced due to the particles

travelling nearly parallel to the wall surface

• Additional model means more modeling parameters to tune

• Erosion-MDM can be coupled and more realistic results can be

obtained


erosion analysis of subsea equipment: a case study with high solid loading

Documents

erosion wear

erosion models prospect

primary erosion models

erosion of pristine

mmyrcontours of erosion

erosion prediction jobs

erosion of worn geometry22

typical erosion problems22